ε-Caprolactam is an important chemical material that can be used as a material for polyamides and the like, and is industrially produced worldwide. It is mostly used as a material for Nylon 6 which is a polyamide.
As an industrial production method of ε-caprolactam, a production method using the Beckmann rearrangement reaction with fuming sulfuric acid from cyclohexanone oxime has been widely employed. That production method uses crude oil as the original material. From the viewpoint of possible depletion of fossil resources in the future, and the problem of global warming due to emission of greenhouse gases by mining and use of fossil resources, development of a method of producing ε-caprolactam using an alternative material is necessary. In particular, development of methods of producing ε-caprolactam from biomass, which is a renewable resource, or from a substance derivable from biomass resources, has been demanded.
WO 2013/126250 discloses a method of producing ε-caprolactam by reacting adipic acid with hydrogen and ammonia in the presence of a heterogeneous catalyst and tert-butanol. As disclosed in JP 2011-515111 A and Biotechnology and Engineering, vol. 111, pp. 2580-2586(2011), adipic acid is a substance that is derivable from biomass resources because it can be produced from sugar by fermentation.
WO 2012/141997 also discloses a method of producing ε-caprolactam by reacting muconic acid with hydrogen and ammonia in the presence of a catalyst. As disclosed in US 2013/0030215 A1, muconic acid is a substance that is derivable from biomass resources and can be produced from glucose by fermentation.
3-Oxoadipic acid is a C6 dicarboxylic acid having a carbonyl group. JP 2012-59 A discloses a method in which 3-oxoadipic acid is produced from protocatechuic acid or vanillic acid by fermentation. Natural Product Reports, vol. 28, pp. 1883-1896(2011) discloses that protocatechuic acid and vanillic acid can be obtained by the decomposition of lignin which is a major component of plants. Journal of the American Chemical Society, vol. 117, pp. 2395-2400(1995) discloses a method in which protocatechuic acid is produced from glucose by fermentation. It can thus be said that 3-oxoadipic acid is derivable from lignin or sugar.
WO 2014/043182 discloses a method of producing 3-hydroxyadipic acid by reacting 3-oxoadipic acid with hydrogen in the presence of a catalyst and a solvent.
By the method disclosed in WO 2013/126250, ε-caprolactam can be produced from adipic acid. However, adipic acid is considered to have a low efficiency in the derivation thereof from biomass resources and is not preferred as a biomass-resource material for ε-caprolactam. For example, JP 2011-515111 A discloses a method of producing adipic acid from glucose by fermentation, but does not describe any actual working example of producing adipic acid, and it is unclear whether or not the method can actually produce adipic acid. In general, when a substance is produced using a microorganism, it is desirable that oxidation-reduction balance determined by the ratio of NADH to NAD+ in cells be maintained, but that suggests that the oxidation-reduction balance is not maintained, and thus it is thought that such a method is difficult to produce adipic acid. According to the method disclosed in Biotechnology and Engineering, vol. 111, pp. 2580-2586(2011), the yield of adipic acid on the basis of glucose is 0.008 mol %, which is low.
By the method disclosed in WO 2012/141997, ε-caprolactam can be produced from muconic acid. However, muconic acid has a low efficiency in the derivation thereof from biomass resources and is not preferred as a material for ε-caprolactam. According to the method disclosed in US 2013/0030215 A1, the yield of muconic acid on the basis of glucose is 30 mol %, which is low and not a sufficiently satisfactory value.
In contrast, 3-oxoadipic acid can be derived from biomass resources at a high efficiency. According to the method disclosed in JP 2012-59 A, the yield of 3-oxoadipic acid is 100 mol % on the basis of protocatechuic acid or vanillic acid which is a lignin decomposition product. According to the method disclosed in Journal of the American Chemical Society, vol. 117, pp. 2395-2400(1995), the yield of protocatechuic acid on the basis of glucose is 50 mol %. From the aforementioned descriptions, it is considered that 3-oxoadipic acid is a substance derivable from a lignin decomposition product or glucose at a high efficiency, and is preferred as a material for ε-caprolactam which is derivable from biomass resources.
However, there has been no report hitherto on a method of converting 3-oxoadipic acid into ε-caprolactam. 3-Oxoadipic acid is a compound whose basic structure is a C6 dicarboxylic acid similar to adipic acid and muconic acid. However, as shown in Comparative Example 1 herein, the direct application of the method described in WO 2012/141997 to 3-oxoadipic acid was found not to produce ε-caprolactam at all. In other words, it turned out that a method of converting muconic acid to ε-caprolactam cannot be applied directly to 3-oxoadipic acid.
It could therefore be helpful to provide a method of producing ε-caprolactam from 3-oxoadipic acid which is preferred as a biomass resource.